The present invention relates to an apparatus for testing the adhesion strength of a hot-melt adhesive for use in adhesion between corrugated boards.
With a conventional apparatus for testing hot-melt adhesion strength, a testing process comprises steps of applying a predetermined amount of adhesives to one test piece, pressing said one test piece on other test piece with an actuator such as air cylinders into close contact therewith after a determined period of time, and peeling the one test piece from the other test piece after the passage of a period of time so that the adhesion strength of the hold-melt adhesive may be determined in view of the resultant tensile force. During said process, the test piece is held by gripping one end of the test piece by means of a clamp.
For sticking a first test piece with an adhesive applied thereto on a second test piece, said conventional apparatus for test of adhesion strength is designed to perform both operations of bringing the test pieces toward each other and putting them into close contact with each other in one procedure step using one and the same air cylinder. This makes it difficult to accurately control the bonding pressure during such a bonding operation.
Furthermore, with the conventional testing apparatus, the detection of a load applied to the test piece is effected by a load cell attached to the actuator which is used to lift the test piece, thereby to render difficult precise measurement of any pressure applied between the test pieces during the bonding operation while during the peeling operation, a load can be detected only when it reaches its peak value.
As described above, the test piece is fixedly secured at its one end by the clamp, and so the test pieces are easily subjected to deformation at the time of pressure contact as well as peeling. In order to avoid such inconveniences, use is made of a boxboard, plastic plate, metallic plate, etc., having a high flexural strength as a test piece. For this reason, the above mentioned test is considered to be less practical in case the hot-melt adhesive is used in adhesion of corrugated boards, and thus, any test result obtained is deemed less reliable.